Installing Minecraft (version 1.3.1) on Linux is not always as simple as you might think. It's a Java application so it should run on all platforms supported by Oracle but unfortunately sometimes (For some unknown reasons) this doesn't work out of the box. This article describes how to get it running on a current Ubuntu Linux 12.04 on a 64 bit machine and how to create a desktop entry for it so you don't have to start it with this long command mentioned on the Minecraft website.